In recent years, the definition of a display unit is becoming higher and the size is becoming larger, so that noise at the time of driving, which exerts an influence on the quality of a video image displayed in the display unit is an issue. To reduce such noise, in a liquid crystal display device, the display quality of a video image is improved by performing dot-reversal driving or column-reversal driving in which a DC voltage is applied to an opposed electrode in each pixel and a positive video signal and a negative video signal are alternately applied to source signal lines.
However, the polarity of the video signal supplied to the source signal lines needs to be reversed every frame period. Particularly, in the dot-reversal driving, the polarity of the video signal also needs to be reversed every horizontal period (1H). In the case of reversing the polarity of the video signal as described above, the polarity of a driver video amplifier needs to be switched each time to increase the swing width of the video signal, so that the power consumption increases.
For example, as described in Patent Documents 1 and 2, a discharge circuit is provided for every two adjacent source signal lines, and the discharge circuits are simultaneously made conductive every horizontal period. At this time, a positive video signal is supplied to one of the source signal lines, and a negative video signal is supplied to the other source signal line. By making the signal lines conductive, charge sharing is performed between the adjacent source signal lines. By the charge sharing, the swing width of a video signal necessary at the time of reversing the polarity of the video signal decreases, so that the power consumption is reduced.